As compared to other display devices such as liquid crystal display (LCD) devices, the organic light emitting diode (OLED) display apparatuses are self-emitting apparatuses that do not require a backlight. Having the advantages of fast response, a wider viewing angle, high brightness, more vivid color rendering, thinner and lighter, they have found a wide range of applications in display field.
Typically, an OLED display apparatus includes an anode, one or more organic functional layers and a cathode. The one or more organic functional layers typically includes a light emitting layer (EML), and optionally one or more of a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), and an electrode injection layer (EIL). When a voltage is applied between the cathode and the anode, charge carriers (electrons and holes) are injected from the cathode and the anode into the light emitting layer. The electrons and holes are recombined in the light emitting layer, which emits light.